Dosimeters are utilized to detect contaminants over long time durations and are used, for example, for monitoring a workplace. The dosimeters take up and collect the substance to be detected over the particular time duration so that the detected substance can be subjected to an evaluation at the end of the collection period.
A dosimeter of this kind is disclosed in U.S. Pat. No. 3,992,153. This dosimeter utilizes an oxidizing reagent for detecting nitrogen which stores the substance to be detected such as gaseous NO.sub.2 by converting into NO.sub.3 -ions. For evaluation, ion-selective electrodes are introduced into the solvent and the collected ion concentration is determined by means of a voltage measurement. The quantity of the gaseous contaminant taken up during the collection time can be arrived at by conversion and inference.
Another dosimeter is described in copending application Ser. No. 341,579, filed on Apr. 21, 1989, which is incorporated herein by reference. This application discloses an electrochemical dosimeter by means of which substances can be detected via a conductivity measurement.
For the known dosimeter, it is disadvantageous that it cannot be utilized for further use after the evaluation. At least the electrolyte or the detecting solution must be exchanged for a new and unused one for which complex and carefully manipulated steps are required. Especially when filling the electrolyte chamber, care must be taken that the electrolyte quantity is very precisely measured because otherwise the measurements are not reproducible. Used dosimeters are destroyed since these steps, as a rule, cannot be carried out by operating personnel or the user. This leads to increased operating costs and to a burden for the environment because of the used solutions or electrolytes.
Dosimeters must be calibrated and their operating capability must be checked for a successful use thereof. For the known dosimeter, this can only be done in a random manner because each time the electrolyte solution is rendered unusable for measurement. The non-calibrated or non-tested dosimeters provided for measuring use can therefore only be evaluated on a probability basis.